Radiation curable resin composition and rapid three dimensional imaging process using the same

ABSTRACT

The invention relates to a radiation curable resin composition comprising a cationically polymerizable component, a cationic photoinitiator, a hydroxy component, and an impact modifier. The resin composition can preferably be used in the preparation of three dimensional objects.

CROSS-REFERENCE

This is a continuation of application Ser. No. 12/667,108, filed 12 Aug.2010, which is a U.S. national phase application of InternationalApplication No. PCT/EP2007/003676 filed 26 Apr. 2007 which designatedthe U.S. and claims priority to U.S. Provisional Applications No.60/796,197 filed 1 May 2006 and No. 60/907,002 filed 16 Mar. 2007, eachof which are hereby incorporated by reference in their entirety as iffully set forth herein.

FIELD OF THE INVENTION

The present invention relates to radiation curable compositions whichare particularly suitable for the production of three-dimensional shapedarticles by means of layerwise imaging methods, such asstereolithography, 3D printing and Digital Light Processing, to aprocess for the production of a cured product and, in particular, forthe stereolithographic production of three dimensional shaped articlesfrom this composition having excellent mechanical properties.

BACKGROUND OF THE INVENTION

The production of three-dimensional articles of complex shape by meansof stereolithography has been known for a number of years. In thistechnique the desired shaped article is built up from aradiation-curable composition with the aid of a recurring, alternatingsequence of two steps (a) and (b). In step (a), a layer of theradiation-curable composition, one boundary of which is the surface ofthe composition, is cured with the aid of appropriate imaging radiation,preferably imaging radiation from a computer-controlled scanning laserbeam, within a surface region which corresponds to the desiredcross-sectional area of the shaped article to be formed, and in step (b)the cured layer is covered with a new layer of the radiation-curablecomposition, and the sequence of steps (a) and (b) is repeated until aso-called green model of the desired shape is finished. This green modelis, in general, not yet fully cured and may therefore be subjected topost-curing, though such post curing is not required.

Via an equivalent process, photopolymer can be jetted by inkjet ormultiple ink jet processes in an imagewise fashion. While jetting thephotopolymer or after the photopolymer is applied actinic exposure canbe provided to initiate polymerization. Multiple materials (for examplenon-reactive waxes, weakly reacting photopolymers, photopolymers ofvarious physical properties, photopolymers with various colors or colorformers, etc.) can be jetted or applied to provide supports or alternatecured properties. An alternative process is Digital Light Processing,wherein where by an entire layer can be radiation cured simultaneously.

The mechanical strength of the green model (modulus of elasticity,fracture strength), also referred to as green strength, constitutes animportant property of the green model and is determined essentially bythe nature of the stereolithographic-resin composition employed incombination with the type of stereolithography apparatus used and degreeof exposure provided during part fabrication. Other important propertiesof a stereolithographic-resin composition include a high sensitivity forthe radiation employed in the course of curing and a minimum amount ofcurl or shrinkage deformation, permitting high shape definition of thegreen model. In addition, for example, it should be relatively easy tocoat a new layer of the stereolithographic resin composition during theprocess. Of course, not only the green model but also, and even moreimportant, the final cured article should have optimum mechanicalproperties meeting with the end-use requirements.

The developments in this area of technology move towards compositionshaving better mechanical properties in order to better simulateproperties of commodity materials like polypropylene and engineeringtype polymers like e.g. polyamides (PA6, PA66, . . . ) and polyesters(PET, PBT). Also there exists a requirement for faster cure and processspeeds, so as to decrease the time to build a part. This has resulted innew stereolithography machines having solid state lasers that have ahigh energy output, very fast laser-scanning and faster recoatingprocesses. The new machines supply UV light with a power around 800 mWand above, compared to 200-300 mW for the older conventional machines.Also the scanning time is reduced by 3 to 4 times. These high powers,high scanning speeds, and short recoating times result in highertemperatures, due to polymerization exotherm of the resins and partsduring fabrication. Typical temperatures have risen to values between 50and 90° C., which may lead to part distortion and excessive colordevelopment.

Several patent publications are known that describe resin compositionsthat can be used in rapid prototyping and aim at improving mechanicalproperties of the three dimensional articles. Examples of such patentpublications are EP 831127, EP 848294, EP 938026, EP 1437624, JP2003-238691, U.S. Pat. No. 6,833,231, US2003-198824, US 2004-013977, US2005-072519, US 2005-0175925, WO 9950711, WO 0063272, WO 04111733 and WO04113395. Sometimes articles are produced that have a high (tensile)modulus, but these articles have a low toughness/impact resistance.Other references provide articles having high impact resistance, butthey have a very low modulus. Resin compositions that give after fullcure an article that possesses both a high modulus and a high impactresistance are not disclosed in literature.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide resin compositionsthat after full cure show high (tensile) modulus and high toughness asshown by high impact strength and/or high resistance against crackpropagation (fracture toughness).

A second object of the invention is to provide photocurable resincompositions useful for production of three-dimensional parts withcomplex geometries and excellent mechanical properties.

Another object of the invention is to provide photocurable resincompositions that can be used for rapid manufacture of durable customand semi-custom parts.

A further object of the invention is to provide resin compositions thatcan be easily used in stereolithography machines.

SUMMARY OF THE INVENTION

The present invention relates to a radiation curable compositioncomprising

-   -   a. a cationically polymerizable component    -   b. a cationic photoinitiator    -   c. a hydroxy component    -   d. an impact modifier    -   wherein the resin composition after full cure has a tensile        modulus of >2 GPa; a yield stress <70 MPa; and a K_(1C)        value >1.3 MPa·(m)^(1/2) or an Izod value >0.45 J/cm.        Another embodiment of the present invention relates to a        radiation curable composition comprising    -   a. 5-90 wt % of an epoxy functional component    -   b. 0.1-10 wt % of a cationic photoinitiator    -   c. 1-35 wt % of a polyol    -   d. 1-30 wt % of core shell particles    -   e. 1-35 wt % of a compound having at least one (meth)acrylate        group    -   f. 0.1-15 wt % of a radical photoinitiator    -   g. 0-25 wt % of a compound having at least one radically curable        group and one cationically curable group,    -   wherein the epoxy/hydroxy ratio of the composition is in the        range from 2-5, the epoxy/(meth)acrylate ratio is in the range        from 4.5-15 and the aromatic/cycloaliphatic content is between        0.2 and 0.6.

DETAILED DESCRIPTION OF THE INVENTION (A) Cationically PolymerizableComponent (A1) Epoxies

The cationically polymerizable component preferably contains at leastone epoxy-group containing component. The epoxide-containing componentsthat are used in the compositions, according to this invention, arecompounds that possess on average at least one 1,2-epoxide group in themolecule. By “epoxide” is meant the three-membered ring

The epoxide-containing components, also referred to as epoxy materials,are cationically curable, by which is meant that polymerization and/orcrosslinking and other reaction of the epoxy group is initiated bycations. The materials can be monomeric, oligomeric or polymeric and aresometimes referred to as “resins.” Such materials may have an aliphatic,aromatic, cycloaliphatic, arylaliphatic or heterocyclic structure; theycomprise epoxide groups as separate groups, or those groups form part ofan alicyclic or heterocyclic ring system. Epoxy resins of those typesare generally known and are commercially available.

The epoxide-containing material (a) should comprise at least one liquidcomponent such that the combination of materials is a liquid. Thus, theepoxide-containing material can be a single liquid epoxy material, acombination of liquid epoxy materials, or a combination of liquid epoxymaterial(s) and solid epoxy material(s) which is soluble in the liquid.

Examples of suitable epoxy materials include polyglycidyl andpoly(methylglycidyl) esters of polycarboxylic acids, orpoly(oxiranyl)ethers of polyethers. The polycarboxylic acid can bealiphatic, such as, for example, glutaric acid, adipic acid and thelike; cycloaliphatic, such as, for example, tetrahydrophthalic acid; oraromatic, such as, for example, phthalic acid, isophthalic acid,trimellitic acid, or pyromellitic acid. The polyether can bepoly(tetramethylene oxide). It is likewise possible to usecarboxyterminated adducts, for example, of trimellitic acid and polyols,such as, for example, glycerol or 2,2-bis(4-hydroxycyclohexyl)propane.

Suitable epoxy materials also include polyglycidyl orpoly(-methylglycidyl)ethers obtainable by the reaction of a compoundhaving at least one free alcoholic hydroxy groups and/or phenolichydroxy groups and a suitably substituted epichlorohydrin. The alcoholscan be acyclic alcohols, such as, for example, ethylene glycol,diethylene glycol, and higher poly(oxyethylene) glycols; cycloaliphatic,such as, for example, 1,3- or 1,4-dihydroxycyclohexane,bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane, or1,1-bis(hydroxymethyl)cyclohex-3-ene; or contain aromatic nuclei, suchas N,N-bis(2-hydroxyethyl)aniline orp,p′-bis(2-hydroxyethylamino)diphenylmethane.

The epoxy compounds may also be derived from mononuclear phenols, suchas, for example, from resorcinol or hydroquinone, or they may be basedon polynuclear phenols, such as, for example,bis(4-hydroxyphenyl)methane (bisphenol F),2,2-bis(4-hydroxyphenyl)propane (bisphenol A), or on condensationproducts, obtained under acidic conditions, of phenols or cresols withformaldehyde, such as phenol novolacs and cresol novolacs.

Examples of suitable epoxy materials include poly(S-glycidyl) compoundswhich are di-S-glycidyl derivatives which are derived from dithiols,such as, for example, ethane-1,2-dithiol orbis(4-mercaptomethylphenyl)ether.

Other examples of suitable epoxy materials includebis(2,3-epoxycyclopentyl)ether, 2,3-epoxy cyclopentyl glycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane, bis(4-hydroxycyclohexyl)methanediglycidyl ether, 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate,di(3,4-epoxycyclohexylmethyl)hexanedioate,di(3,4-epoxy-6-methylcyclohexylmethyl)hexanedioate,ethylenebis(3,4-epoxycyclohexanecarboxylate),ethanedioldi(3,4-epoxycyclohexylmethyl)ether, vinylcyclohexene dioxide,dicyclopentadiene diepoxide, α-(oxiranylmethyl)-ω-(oxiranylmethoxy)poly(oxy-1,4-butanediyl), diglycidyl ether of neopentyl glycol, or2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-1,3-dioxane, andcombinations thereof.

It is, however, also possible to use epoxy resins in which the 1,2-epoxygroups are bonded to different heteroatoms or functional groups. Thosecompounds include, for example, the N,N,O-triglycidyl derivative of4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5-dimethylhydantoin, or2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

In addition, liquid prereacted adducts of such epoxy resins withhardeners are suitable for epoxy resins.

It is of course also possible to use mixtures of epoxy materials in thecompositions according to the invention.

Preferred epoxy materials are cycloaliphatic diepoxides. Especiallypreferred are 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,and combinations thereof. Other preferred epoxy materials are based onpolynuclear phenols, such as, for example, bis(4-hydroxyphenyl)methane(bisphenol F), 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), oroligomers thereof. The epoxy materials can have molecular weights whichvary over a wide range. In general, the epoxy equivalent weight, i.e.,the number average molecular weight divided by the number of reactiveepoxy groups, is preferably in the range of 44 to 1000.

(A2) Oxetane Group Containing Component

The compositions of the present invention may also contain oxetanes ascationically polymerizable component. An oxetane compound comprises atleast one oxetane ring shown by the following formula (1).

The oxetane compound can be polymerised or crosslinked by irradiationwith light in the presence of a cationically polymerizablephotoinitiator.

Examples of oxetanes having one oxetane ring in the molecule are shownby the following formula (2):

wherein Z represents an oxygen atom or sulphur atom; R1 represents ahydrogen atom, fluorine atom, an alkyl group having 1-6 carbon atomssuch as a methyl group, ethyl group, propyl group, and butyl group, afluoroalkyl group having 1-6 carbon atoms such as trifluoromethyl group,perfluoroethyl group, and perfluoropropyl group, an aryl group having6-18 carbon atoms such as a phenyl group and naphthyl group, a furylgroup, or a thienyl group; and R2 represents a hydrogen atom, an alkylgroup having 1-6 carbon atoms for example a methyl group, ethyl group,propyl group, and butyl group, an alkenyl group having 2-6 carbon atomsfor example a 1-propenyl group, 2-propenyl group, 2-methyl-1-propenylgroup, 2-methyl-2-propenyl group, 1-butenyl group, 2-butenyl group, and3-butenyl group, an aryl group having 6-18 carbon atoms for example aphenyl group, naphthyl group, anthranyl group, and phenanthryl group, asubstituted or unsubstituted aralkyl group having 7-18 carbon atoms forexample a benzyl group, fluorobenzyl group, methoxy benzyl group,phenethyl group, styryl group, cynnamyl group, ethoxybenzyl group, agroup having other aromatic rings for instance an aryloxyalkyl forexample a phenoxymethyl group and phenoxyethyl group, an alkylcarbonylgroup having 2-6 carbon atoms for example an ethylcarbonyl group,propylcarbonyl group, butylcarbonyl group, an alkoxy carbonyl grouphaving 2-6 carbon atoms for example an ethoxycarbonyl group,propoxycarbonyl group, butoxycarbonyl group, an N-alkylcarbamoyl grouphaving 2-6 carbon atoms such as an ethylcarbamoyl group, propylcarbamoylgroup, butylcarbamoyl group, pentylcarbamoyl group, or a polyethergrouphaving 2-1000 carbon atoms.

Examples of oxetane compounds having two oxetane rings in the moleculeare compounds shown by the following formula (3):

wherein R1 is the same as defined for the above formula (2); R3represents a divalent organic group, like for example a linear orbranched alkylene group having 1-20 carbon atoms for example an ethylenegroup, propylene group, and butylene group, a linear or branchedpoly(alkyleneoxy) group having 1-120 carbon atoms for example apoly(ethyleneoxy) group and poly(propyleneoxy) group, a linear orbranched unsaturated hydrocarbon group for example a propenylene group,methylpropenylene group, and butenylene group.

As specific examples of the compounds having two oxetane rings in themolecule, compounds shown by the following formulas (9), and (10) can begiven.

In the formula (10), R1 is the same as defined for the above formula(2).

Specific examples of oxetane compounds are given below.

Compounds containing one oxetane ring in the molecule:3-ethyl-3-hydroxymethyloxetane, 3-(meth)allyloxymethyl-3-ethyloxetane,(3-ethyl-3-oxetanylmethoxy)methylbenzene,(3-ethyl-3-oxetanylmethoxy)benzene,4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene,4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene,[1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether, isobutoxymethyl(3-ethyl-3-oxetanylmethyl)ether, isobornyloxyethyl(3-ethyl-3-oxetanylmethyl)ether, isobornyl(3-ethyl-3-oxetanylmethyl)ether, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl)ether, ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl)ether,dicyclopentadiene (3-ethyl-3-oxetanylmethyl)ether,dicyclopentenyloxyethyl (3-ethyl-3-oxetanyl methyl)ether,dicyclopentenyl (3-ethyl-3-oxetanylmethyl)ether, tetrahydrofurfuryl(3-ethyl-3-oxetanylmethyl)ether, tetrabromophenyl(3-ethyl-3-oxetanylmethyl)ether, 2-tetrabromophenoxyethyl(3-ethyl-3-oxetanylmethyl)ether, tribromophenyl(3-ethyl-3-oxetanylmethyl)ether, 2-tribromophenoxyethyl(3-ethyl-3-oxetanylmethyl)ether, 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl)ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl)ether,butoxyethyl (3-ethyl-3-oxetanylmethyl) ether, pentachlorophenyl(3-ethyl-3-oxetanylmethyl)ether, pentabromophenyl(3-ethyl-3-oxetanylmethyl)ether, bornyl (3-ethyl-3-oxetanylmethyl)ether.

Compounds containing two or more oxetane rings in the molecule:3,7-bis(3-oxetanyl)-5-oxa-nonane,3,3′-(1,3-(2-methylenyl)propanediylbis(oxymethylene))bis-(3-ethyloxetane),1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane,1,3-bis[(3-ethyl-3-oxetanylmethoxy)methy]propane, ethylene glycolbis(3-ethyl-3-oxetanylmethyl)ether, dicyclopentenylbis(3-ethyl-3-oxetanylmethyl)ether, triethylene glycolbis(3-ethyl-3-oxetanylmethyl)ether, tetraethylene glycolbis(3-ethyl-3-oxetanylmethyl)ether, tricyclodecanediyldimethylene(3-ethyl-3-oxetanylmethyl)ether, trimethylolpropanetris(3-ethyl-3-oxetanylmethyl)ether,1,4-bis(3-ethyl-3-oxetanylmethoxy)butane,1,6-bis(3-ethyl-3-oxetanylmethoxy)hexane, pentaerythritoltris(3-ethyl-3-oxetanylmethyl)ether, pentaerythritoltetrakis(3-ethyl-3-oxetanylmethyl) ether, polyethylene glycolbis(3-ethyl-3-oxetanylmethyl)ether, dipentaerythritolhexakis(3-ethyl-3-oxetanylmethyl)ether, dipentaerythritolpentakis(3-ethyl-3-oxetanylmethyl)ether, dipentaerythritoltetrakis(3-ethyl-3-oxetanylmethyl)ether, caprolactone-modifieddipentaerythritol hexakis(3-ethyl-3-oxetanylmethyl)ether,caprolactone-modified dipentaerythritolpentakis(3-ethyl-3-oxetanylmethyl)ether, ditrimethylolpropanetetrakis(3-ethyl-3-oxetanylmethyl)ether, EO-modified bisphenol Abis(3-ethyl-3-oxetanylmethyl)ether, PO-modified bisphenol Abis(3-ethyl-3-oxetanylmethyl)ether, EO-modified hydrogenated bisphenol Abis(3-ethyl-3-oxetanylmethyl)ether, PO-modified hydrogenated bisphenol Abis(3-ethyl-3-oxetanylmethyl)ether, EO-modified bisphenol F(3-ethyl-3-oxetanylmethyl)ether. These compounds can be used eitherindividually or in combination of two or more.

Preferred oxetanes are selected from the group consisting of componentsdefined by formula 2, wherein R¹ is a C1-C₄ alkyl group, Z=Oxygen andR²═H, a C1-C8 alkyl group or a phenylgroup;3-ethyl-3-hydroxymethyloxetane,(3-ethyl-3-oxetanylmethoxy)methylbenzene,(3-ethyl-3-oxetanylmethoxy)benzene, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl)ether, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane,1,3-bis[(3-ethyl-3-oxetanylmethoxy)methyl]propane, ethylene glycolbis(3-ethyl-3-oxetanylmethyl)ether andbis(3-ethyl-3-oxetanylmethyl)ether.

The oxetane compounds can be used either individually or in combinationsof two or more.

(A3) Other Cationically Polymerizable Components

Other cationically polymerizable components that may be used in thecomposition of the present invention include, for instance, cycliclactone compounds, cyclic acetal compounds, cyclic thioether compounds,spiro orthoester compounds, and vinylether compounds.

It is of course possible to use mixtures of cationically polymerizablecomponents in the compositions according to the invention.

In one embodiment of the invention the composition of the invention maycontain cationically polymerizable components having a cationicallycurable group and at least one hydroxyl group. Preferably this componentwill have one cationically curable group and one or more hydroxylgroups. It is believed that such components will also contribute tomaking a three dimensional object having a network with intermediatecross-link density.

Preferably the composition of the present invention comprises, relativeto the total weight of the composition, at least 30 wt %, morepreferably at least 40 wt %, and most preferably at least 60 wt % ofcationically curable components. Preferably the composition of theinvention comprises, relative to the total weight of the composition,less than 90 wt %, and more preferably less than 80 wt % cationicallycurable components.

(B) Cationic Photoinititator

In the compositions according to the invention, any suitable type ofphotoinitiator that, upon exposure to actinic radiation, forms cationsthat initiate the reactions of the cationically polymerizable compounds,such as epoxy material(s), can be used. There are a large number ofknown and technically proven cationic photoinitiators that are suitable.They include, for example, onium salts with anions of weaknucleophilicity. Examples are halonium salts, iodosyl salts or sulfoniumsalts, such as are described in published European patent application EP153904 and WO 98/28663, sulfoxonium salts, such as described, forexample, in published European patent applications EP 35969, 44274,54509, and 164314, or diazonium salts, such as described, for example,in U.S. Pat. Nos. 3,708,296 and 5,002,856. All eight of thesedisclosures are hereby incorporated in their entirety by reference.Other cationic photoinitiators are metallocene salts, such as described,for example, in published European applications EP 94914 and 94915,which applications are both hereby incorporated in their entirety byreference.

A survey of other current onium salt initiators and/or metallocene saltscan be found in “UV Curing, Science and Technology”, (Editor S. P.Pappas, Technology Marketing Corp., 642 Westover Road, Stamford, Conn.,U.S.A.) or “Chemistry & Technology of UV & EB Formulation for Coatings,Inks & Paints”, Vol. 3 (edited by P. K. T. Oldring), and both books arehereby incorporated in their entirety by reference.

Preferred initiators include diaryl iodonium salts, triaryl sulfoniumsalts, or the like. Typical photo-polymerization initiators arerepresented by the following formulae (11) and (12):

whereinQ₃ represents a hydrogen atom, an alkyl group having 1 to 18 carbonatoms, an alkoxyl group having 1 to 18 carbon atoms a thiophenyl groupor a group represented by the formula (12a):

M represents a metal atom, preferably antimony;Z represents a halogen atom, preferably fluorine; andt is the valent number of the metal, for example 6 in the case ofantimony.

Preferred cationic photoinitiators include iodonium photoinitiators,e.g. iodonium tetrakis (pentafluorophenyl) borate, because they tend tobe less yellowing, especially when used in combination withphotosensitizers such as, for instance, n-ethyl carbazole.

In order to increase the light efficiency, or to sensitize the cationicphotoinitiator to specific wavelengths, such as for example specificlaser wavelengths or a specific series of laser wavelengths, it is alsopossible, depending on the type of initiator, to use sensitizers.Examples are polycyclic aromatic hydrocarbons or aromatic ketocompounds. Specific examples of preferred sensitizers are mentioned inpublished European patent application EP 153904. Other preferredsensitizers are benzoperylene, 1,8-diphenyl-1,3,5,7-octatetraene, and1,6-diphenyl-1,3,5-hexatriene as described in U.S. Pat. No. 5,667,937,which is hereby incorporated in its entirety by reference. It will berecognized that an additional factor in the choice of sensitizer is thenature and primary wavelength of the source of actinic radiation.

Preferably, the present composition comprises, relative to the totalweight of the composition, 0.1-0.15 wt % of one or more cationicphotoinitiators, more preferably 1-10 wt %.

(C) Hydroxy Functional Components

The composition of the invention contains at least one hydroxycomponent, which is a polyol having at least 2 hydroxyl groups. Thehydroxy component used in the present invention is a polyol which maycontain primary and/or secondary hydroxyl groups. It is preferred thatthe hydroxyl component contains at least one primary hydroxyl group.Primary hydroxyl groups are OH-groups, which are covalently bonded to acarbon atom having 2 or 3 hydrogen atoms. Preferably the hydroxycomponent contains two primary hydroxyl groups. In another preferredembodiment of the present invention the hydroxy component is a compoundhaving primary hydroxyl groups and/or secondary hydroxyl groups locatedat the terminus of an alkyl or alkoxy chain, wherein the alkyl or alkoxychain may have from 1 to 100 C-atoms, preferably from 2 to 50 C atoms,more preferably from 5-40 C atoms. While not wishing to be bound bytheory, we believe these primary and secondary hydroxyl groupspreferably function as chain transfer agents in the cationicpolymerization reaction. Mixtures of different hydroxyl compounds mayalso be used.

The hydroxyl component may be a did of molecular weight less than 200wherein preferably one, and more preferably both, hydroxyl groups areprimary hydroxyl groups. Examples of suitable dots include: ethyleneglycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol,triethyleneglycol, tetraethylene glycol, dipropylene glycol andtripropylene glycol.

The hydroxy component preferably is a molecule that has a centralstructure to which have been added chain extensions of, for example,ethylene oxide or propylene oxide. Preferably the hydroxy component isan alkoxylated polyol or an alkoxylated aromatic diol. More preferablythe hydroxy component is an ethoxylated polyol or ethoxylated aromaticdiol.

Examples of suitable hydroxy components are oligomeric and polymerichydroxyl-containing materials include polyoxyethylene andpolyoxypropylene glycols and triols of molecular weights from about 200to about 1500 g/mol; polytetramethylene glycols of varying molecularweight; poly(oxyethylene-oxybutylene) random or block copolymers;hydroxy-terminated polyesters and hydroxy-terminated polylactones;hydroxy-functionalized polyalkadienes, such as polybutadiene; aliphaticpolycarbonate polyols, such as an aliphatic polycarbonate diol;hydroxy-terminated polyethers; and alkoxylated aromatic diolsrepresented by the chemical structure shown:

-   -   wherein R3=—CH₂—, —C(CH₃)₂—, —C(CF₃)₂—, —CCl₂—, —O—, —S—, and        R4=—CH₂CH₂— or —CH₂CH(CH₃)—, and n and m are 1 through 10.

In one embodiment of the invention, the hydroxy component preferablycomprises an ethoxylated bisphenol A. The ethoxylated bisphenol A mayfor example contain between 1 and 30 ethoxylations per hydroxyl group,preferably from 2 to 20 ethoxylations per hydroxyl group. In anotherembodiment of the invention, the hydroxy component preferably comprisesa propoxylated bisphenol A. The propoxylated bisphenol A may for examplecontain between 1 and 30 propoxylations per hydroxyl group, preferablyfrom 2 to 20 propoxylations per hydroxyl group.

In yet another embodiment of the invention, the hydroxy componentpreferably comprises a bisphenol A with mixed ethoxylations andpropoxylations. This bisphenol A may for example contain in totalbetween 1 and 30 ethoxylations and/or propoxylations per hydroxyl group,preferably from 2 to 20 ethoxylations/propoxylations per hydroxyl group.

Other preferred hydroxyl components are polyether polyols obtained bymodifying a polyhydric alcohol containing three or more hydroxyl groups,such as trimethylolpropane, glycerol, pentaerythritol, sorbitol,sucrose, or quadrol, with a cyclic ether compound, such as ethyleneoxide (EO), propylene oxide (PO), butylene oxide, or tetrahydrofuran.Specific examples include EO-modified trimethylolpropane, PO-modifiedtrimethylolpropane, tetrahydrofuran-modified trimethylolpropane,EO-modified glycerol, PO-modified glycerol, tetrahydrofuran-modifiedglycerol, EO-modified pentaerythritol, PO-modified pentaerythritol,tetrahydrofuran-modified pentaerythritol, EO-modified sorbitol,PO-modified sorbitol, EO-modified sucrose, PO-modified sucrose, andEO-modified quadrol. Of these, EO-modified trimethylolpropane,PO-modified trimethylolpropane, EO-modified glycerol, and PO-modifiedglycerol are preferable.

The molecular weight of the hydroxyl component is preferably 100-1500,and more preferably 160-1000 g/mol. The proportion of the hydroxylcomponent used in the liquid photocurable resin composition of thepresent invention is usually 1-35 wt %, preferably 5-30 wt %, andparticularly preferably 5-25 wt %.

(D) Impact Modifier

The composition of the present invention comprises at least one impactmodifier. Examples of suitable impact modifiers are elastomers and, morepreferably, pre-fabricated elastomer particles. These elastomers have aglass transition temperature (Tg) lower than 0° C., as determined withDSC.

The composition according to the present invention preferably contains1-30 wt % impact modifier. The impact modifier preferably compriseselastomer particles having an average size between 10 nm and 10 μm.

(D1) Elastomers

Given as examples of impact modifying component (D), which can bedispersed into the radiation curable resin composition, are elastomersbased on copolymers of ethylene or propylene and one or more C2 to C12α-olefin monomers.

Examples of such are ethylene/propylene copolymers or ethylene/propylenecopolymers, optionally containing a third copolymerizable diene monomer(EPDM), such as 1,4-hexadiene, dicyclopentadiene, di-cyclooctadiene,methylene norbornene, ethylidene norbornene and tetrahydroindene;ethylene/α-olefin copolymers, such as ethylene-octene copolymers andethylene/α-olefin/polyene copolymers.

Other suitable elastomers are polybutadiene, polyisoprene,styrene/butadiene random copolymer, styrene/isoprene random copolymer,acrylic rubbers (e.g. polybutylacrylate), ethylene/acrylate randomcopolymers and acrylic block copolymers,styrene/butadiene/(meth)acrylate (SBM) block-copolymers,styrene/butadiene block copolymer (styrene-butadiene-styrene blockcopolymer (SBS), styrene-isoprene-styrene block copolymer (SIS) andtheir hydrogenated versions, SEBS, SEPS), and (SIS) and ionomers.

Commercial examples of elastomers are Kraton (SBS, SEBS, SIS, SEBS andSEPS) block copolymers produced by Shell, Lotryl ethyl/acrylate randomcopolymer (Arkema) and Surlyn ionomers (Dupont).

Optionally, the elastomer may be modified to contain reactive groupssuch as e.g. epoxy, oxetane, carboxyl or alcohol. This modification cane.g. be introduced by reactive grafting or by copolymerization.Commercial examples of the latter are the Lotader randomethylene/acrylate copolymers AX8840 (glycidyl methacrylate/GMAmodified), AX8900 and AX8930 (GMA and maleic anhydride modified/MA)produced by Arkema.

Optionally, the elastomer may be crosslinked after mixing into theradiation curable resin composition. The crosslinking structure may beintroduced via a conventional method. As examples of crosslinking agentsused in such a materials peroxide, sulfur, resol and the like,optionally in combination with multifunctional monomers likedivinylbenzene, ethylene glycol di(meth)acrylate, diallylmaleate,triallylcyanurate, triallylisocyanurate, diallylphthalate,trimethylolpropane triacrylate, allyl methacrylate and the like can begiven.

(D2) Pre-Fabricated Elastomer Particles

Examples of a more preferable impact modifier (D) that can be dispersedinto the radiation curable resin composition are pre-fabricatedelastomer particles. Elastomer particles may be prepared by a variety ofmeans, including those obtained by isolation from latex made viaemulsion polymerization, grinding or cryo-grinding of elastomer stock,or preparation in-situ in another component of the composition. Theaverage size of these elastomer particles is preferably between 10 nmand 10 μm.

Examples of commercial sources of such pre-fabricated elastomerparticles are PB (polybutadiene) or PBA (polybutylacrylate) laticesavailable with varying average particle size from various producers, orlatices obtained by emulsification of EPDM, SBS, SIS or any otherrubber.

Optionally, the elastomer may contain a crosslinking structure. Thecrosslinking structure may be introduced by a conventional method. Asexamples of crosslinking agents used in such a material peroxide,sulfur, resol and the like, optionally in combination withmultifunctional monomers like divinylbenzene, ethylene glycoldi(meth)acrylate, diallylmaleate, triallylcyanurate,triallylisocyanurate, diallylphthalate, trimethylolpropane triacrylate,allyl methacrylate, and the like can be given.

Optionally, a shell may be present on the particles that can e.g. beintroduced via grafting or during a second stage of emulsionpolymerization. Examples of such particles are core-shell impactmodifier particles that contain a rubber core and a glassy shell.Examples of core materials are polybutadiene, polyisoprene, acrylicrubber (e.g. polybutylacrylate rubber), styrene/butadiene randomcopolymer, styrene/isoprene random copolymer, or polysiloxane. Examplesof shell materials or graft copolymers are (co)polymers of vinylaromatic compounds (e.g. styrene) and vinyl cyanides (e.g.acrylonitrile) or (meth)acrylates (e.g. MMA).

Optionally, reactive groups can be incorporated into the shell bycopolymerization, such as copolymerisation with glycidyl methacrylate,or by treatment of the shell to form reactive functional groups.Suitable reactive functional groups include, but are not limited to,epoxy groups, oxetane groups, hydroxyl groups, carboxyl groups, vinylether groups, and/or acrylate groups.

Examples of commercially available products of these core-shell typeelastomer particles are Resinous Bond RKB (dispersions of core-shellparticles in epoxy manufactured by Resinous Chemical Industries Co.,Ltd.), Durastrength D400, Durastrength 400R (manufactured by ArkemaGroup), Paraloid EXL-2300 (non-functional shell), Paraloid EXL-2314(epoxy functional shell), Paraloid EXL-2600, Paraloid EXL-3387 andParaloid KM-365 (manufactured by Rohm and Haas), Genioperl P53,Genioperl P23, Genioperl P22 (manufactured by Wacker Chemical) and thelike.

Another example of such elastomer particles are crosslinkedpolyorganosiloxane rubbers that may include dialkylsiloxane repeatingunits, where “alkyl” is C₁-C₅ alkyl. Such particles may be made by themethod disclosed in U.S. Pat. No. 4,853,434 to Block, incorporated inits entirety herein by reference. The particles may be modified toinclude reactive groups such as oxirane, glycidyl, oxetane, hydroxyl,vinyl ester, vinyl ether, or (meth)acrylate groups, or combinationsthereof, preferably on the surface of the particles.

Examples of polyorganosiloxane elastomer particles that are commerciallyavailable are Albidur EP 2240(A), Albidur EP 2640, Albidur VE 3320,Albidur EP 5340, Albidur EP 5640, and Albiflex 296 (dispersions ofparticles in epoxy or vinyl ether resins, Hanse Chemie, Germany),Genioperl M41C (dispersion in epoxy, Wacker Chemical), Chemisnow MXSeries and MP Series (Soken Chemical and Engineering Co.).

Other materials that can be used to make the core/shell particles foruse in the present invention can be found in for example: Nakamura et alJ Appl Polym Sci v 33 n 3 Feb. 20, 1987 p 885-897, 1987, which disclosesa core/shell material with a poly(butyl acrylate) core and poly(methylmethacrylate) shell. The shell has been treated so that it containsepoxide groups; Saija, L. M. and Uminski, M., Surface CoatingsInternational Part B 2002 85, No. B2, June 2002, p. 149-53, whichdescribes a core shell material with core and shell prepared frompoly(methyl methacrylate-co-butyl acrylate), and treated with MMA orAMPS to produce material with carboxylic acid groups on the surface;Aerdts, A. M et al, Polymer 1997 38, No. 16, 1997, p. 4247-52, whichdescribes a material using polystyrene, poly(methyl methacrylate) orpolybutadiene as its core. An epoxidized poly(methyl methacrylate) isused for the shell. The epoxide sites are reactive sites on the core ofthis material.

The core shell particles can include more than one core and/or more thanone shell. In addition, mixtures of core-shell particles with elastomerparticles can be used.

The elastomer particles, or the elastomeric core of the core-shellparticles, preferably have a Tg below 0° C., as determined with DSC.

(D3) Miscible Compounds that Demix into Rubbery Domains Upon Curing.

The compositions according to the present invention may also contain oneor more dissolved components that demix upon curing into rubberydomains. These components generally contain at least one elastomericblock with a Tg below 0° C., which assembles into elastomeric domains.The components may contain functional groups, for example epoxy,hydroxyl, (meth)acrylate, vinyl ether etc. The molecular weight of the(D3) components is in general higher then 1500 g/mol.

Examples of these are epoxy- or carboxyterminated butadiene-nitrilerubbers (ETBN, CTBN). Other examples are epoxy, hydroxy or(meth)acrylate functional low Tg oligomers. In the case where theoligomer is hydroxy-functional, the impact modifier may also act aschain transfer agent and needs to be included in the calculation of thehydroxy content as described in the following paragraph. In this case,it is preferred that also a low molecular weight hydroxy component ispresent in the composition.

Commercial examples of CTBN's are the EPON Resin 58000, e.g. 58003,58005, 58006, 58042, 58901 and 58034. Examples of epoxy- or hydroxyfunctional low Tg oligomers with molecular weight larger then 1500 g/molare the Acclaim series of polypropylene glycols with varying molecularweight (Bayer), the Terathane series of polytetramethylene glycols(Dupont); poly(oxyethylene-oxybutylene) random or block copolymers; pTGLby Hodogaya Chemical Co. Ltd, hydroxy-terminated polyesters andhydroxy-terminated polylactones such as the Placcel 220 series producedby Daicel; hydroxy-functionalized polyalkadienes, such as polybutadiene;aliphatic polycarbonate polyols, such as an aliphatic polycarbonatediol; hydroxy-terminated polyethers or commercially availableepoxide/aliphatic polyol blends such as Uvacure 1530, 1531, 1532, 1533and 1534 (UCB Chemicals). Other examples are Nanostrength blockcopolymers E20, E40 (SBM type) and M22 (full-acrylic) as produced byArkema.

Cationically Polymerizable/Hydroxy Ratio

The composition of the present invention preferably has a cationicallypolymerizable/hydroxy ratio between 2.0 and 5.0. The cationicallypolymerizable/hydroxy ratio (Cat. Poly./Hydroxy) is the amount ofcationically polymerizable functional groups divided by the amount ofhydroxy functional groups present in the composition. The amount ofcationically polymerizable groups is calculated by determining thenumber (mmoles) of cationically polymerizable groups present in 100grams of the composition. Cationically polymerizable groups includeepoxy, oxetane, tetrahydrofuran, cyclic lactone, cyclic acetal, cyclicthioether, Spiro orthoester, and vinylether groups. The amount ofhydroxy groups (or hydroxy value) is calculated by determining thenumber (mmol) of hydroxy groups present in 100 grams of the composition.Only hydroxyl groups present in the cationically polymerizable component(A) and in the hydroxy component (C) (and optionally hydroxyl groupcontaining components (D3)) are taken into account in calculating thehydroxy value. Other components may also contain hydroxy groups (forexample some (meth)acrylate compounds and radical photoinitiators), butthey are not expected to have a strong chain transfer effect on thecationic polymerization and are for this reason and for reasons ofsimplicity kept out of the calculation.

In case the cationically polymerizable groups are epoxy groups, one mayalso describe the cationically polymerizable/hydroxy ratio as theepoxy/hydroxy ratio.

The cationically polymerizable/hydroxy ratio preferably ranges from 2.2to 4.75, and most preferably from 2.4 to 4.5.

(E) Radically Polymerizable Compound

The composition of the present invention may also contain radicallypolymerizable compounds. Suitable examples of radical polymerizablecompounds are compounds having one or more ethylenically unsaturatedgroups, for example compounds having acrylate or methacrylate groups.

Examples of monofunctional ethylenically unsaturated compounds includeisobornyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, ethyldiethylene glycol (meth)acrylate, lauryl(meth)acrylate, dicyclopentadiene (meth)acrylate,dicyclopentenyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate,2-tetrachlorophenoxyethyl (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, tetrabromophenyl (meth)acrylate,2-tetrabromophenoxyethyl (meth)acrylate, 2-trichlorophenoxyethyl(meth)acrylate, tribromophenyl (meth)acrylate, 2-tribromophenoxyethyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, phenoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate,pentachlorophenyl (meth)acrylate, pentabromophenyl (meth)acrylate,polyethylene glycol mono(meth)acrylate, polypropylene glycolmono(meth)acrylate, bornyl (meth)acrylate and, methyltriethylenediglycol (meth)acrylate.

Examples of the polyfunctional radically polymerizable compounds includeethylene glycol di(meth)acrylate, dicyclopentenyl di(meth)acrylate,triethylene glycol diacrylate, tetraethylene glycol di(meth)acrylate,tricyclodecanediyldimethylene di(meth)acrylate, trimethylolpropanetri(meth)acrylate, ethylene oxide (hereinafter may be abbreviated as“EO”) modified trimethylolpropane tri(meth)acrylate, propylene oxide(hereinafter may be abbreviated as “PO”) modified trimethylolpropanetri(meth)acrylate, tripropylene glycol di(meth)acrylate, neopentylglycol di(meth)acrylate, both-terminal (meth)acrylic acid adduct ofbisphenol A diglycidyl ether, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, polyethylene glycoldi(meth)acrylate, dipentaerythritol hexa(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritoltetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate,EO-modified bisphenol A di(meth)acrylate, PO-modified bisphenol Adi(meth)acrylate, EO-modified hydrogenated bisphenol A di(meth)acrylate,PO-modified hydrogenated bisphenol A di(meth)acrylate, EO-modifiedbisphenol F di(meth)acrylate, (meth)acrylate of phenol novolakpolyglycidyl ether, and the like.

Preferred radically polymerizable compounds are selected from the groupconsisting of bisphenol A diglycidylether diacrylate and mono-acrylate,dipentaerithritol hexacrylate and pentacrylate, trimethylolpropanetriacrylate, neopentylglycol propoxylated diacrylate and isobornylacrylate.

Each of the above mentioned radically polymerizable compounds can beused either individually or in combinations of two or more, or incombinations of at least one monofunctional monomer and at least onepolyfunctional monomer.

The content of the radically polymerizable compound that may be used inthe photocurable resin composition of the present invention is usually0-45 wt %, preferably 3-35 wt %. In the case of a hybrid formulation,preferably polyfunctional acrylates, having functionality between 2 and6 are used in the compositions of the present invention in amountsbetween 1 and 30 wt %, more preferably 2-20 wt %, most preferablybetween 3 and 15 wt %, relative to the total composition.

(F) Radical Photoinitiator

The compositions of the present invention may employ one or more freeradical photoinitiators. Examples of photoinitiators include benzoins,such as benzoin, benzoin ethers, such as benzoin methyl ether, benzoinethyl ether, and benzoin isopropyl ether, benzoin phenyl ether, andbenzoin acetate, acetophenones, such as acetophenone,2,2-dimethoxyacetophenone, 4-(phenylthio)acetophenone, and1,1-dichloroacetophenone, benzil, benzil ketals, such as benzil dimethylketal, and benzil diethyl ketal, anthraquinones, such as2-methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone,1-chloroanthraquinone, and 2-amylanthraquinone, also triphenylphosphine,benzoylphosphine oxides, such as, for example,2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO),benzophenones, such as benzophenone, dimethoxybenzophenone,diphenoxybenzophenone, and 4,4′-bis(N,N′-dimethylamino)benzophenone,thioxanthones and xanthones, acridine derivatives, phenazenederivatives, quinoxaline derivatives orI-phenyl-1,2-propanedione-2-O-benzoyloxime, I-aminophenyl ketones or1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,phenyl (1-hydroxyisopropyl)ketone and4-isopropylphenyl(1-hydroxyisopropyl)ketone, or triazine compounds, forexample, 4″′-methyl thiophenyl-1-di(trichloromethyl)-3,5-S-triazine,S-triazine-2-(stilbene)-4,6-bistrichloromethyl, and paramethoxy styryltriazine, all of which are known compounds.

Especially suitable free-radical photoinitiators, which are normallyused in combination with a He/Cd laser, operating at for example 325 nm,an Argon-ion laser, operating at for example 351 nm, or 351 and 364 nm,or 333, 351, and 364 nm, or a frequency tripled YAG solid state laser,having an output of 351 or 355 nm, as the radiation source, areacetophenones, such as 2,2-dialkoxybenzophenones and 1-hydroxyphenylketones, for example 1-hydroxycyclohexyl phenyl ketone,2-hydroxy-1-{4-(2-hydroxyethoxy)phenyl}-2-methyl-1-propanone,benzophenone, or 2-hydroxyisopropyl phenyl ketone (also called2-hydroxy-2,2-dimethylacetophenone), but especially 1-hydroxycyclohexylphenyl ketone. Another class of free-radical photoinitiators comprisesthe benzil ketals, such as, for example, benzil dimethyl ketal.Especially an alpha-hydroxyphenyl ketone, benzil dimethyl ketal, or2,4,6-trimethylbenzoyldiphenylphosphine oxide may be used asphotoinitiator.

Another class of suitable free radical photoinitiators comprises theionic dye-counter ion compounds, which are capable of absorbing actinicrays and producing free radicals, which can initiate the polymerizationof the (meth)acrylates. The compositions according to the invention thatcomprise ionic dye-counter ion compounds can thus be cured in a morevariable manner using visible light in an adjustable wavelength range of400 to 700 nanometers. Ionic dye-counter ion compounds and their mode ofaction are known, for example from published European patent applicationEP 223587 and U.S. Pat. Nos. 4,751,102, 4,772,530 and 4,772,541. Theremay be mentioned as examples of suitable ionic dye-counter ion compoundsthe anionic dye-iodonium ion complexes, the anionic dye-pyryllium ioncomplexes and, especially, the cationic dye-borate anion compounds ofthe following formula (10)

wherein D⁺ is a cationic dye and R₁₂, R₁₃, R₁₄, and R₁₅ are eachindependently of the others alkyl, aryl, alkaryl, allyl, aralkyl,alkenyl, alkynyl, an alicyclic or saturated or unsaturated heterocyclicgroup. Preferred definitions for the radicals R₁₂ to R₁₅ can be found,for example, in published European patent application EP 223587.

Preferred free radical photoinitiators include 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one,2,2-dimethoxyacetophenone, benzophenone and2,4,6-trimethylbenzoyldiphenylphosphine oxide. These photoinitiatorsalone or in combination with each other tend to be comparatively lessyellowing.

Preferably, the present composition comprises, relative to the totalweight of the composition, 0.1-15 wt % of one or more free radicalphotoinitiators, more preferably 1-10 wt %.

Cationically Polymerizable/Radically Polymerizable Ratio.

Compositions which are comprised of radically polymerizable componentsas well as cationically polymerizable components preferably have acationically polymerizable/radically polymerizable ratio between 4 and20. The cationically polymerizable/radically polymerizable ratio is theamount of cationically polymerizable groups divided by the amount ofradically polymerizable functional groups present in the composition.The amount of cationically polymerizable groups is calculated bydetermining the number (mmoles) of cationically polymerizable groupspresent in 100 grams of the composition. The amount of radicallypolymerizable groups is calculated by determining the number (mmol) of(meth)acrylate and other radically polymerizable groups present in 100grams of the composition. The cationically polymerizable/radicallypolymerizable ratio (Cat. Poly./Rad. Poly) is calculated by simplydividing the cationically polymerizable value by the radicallypolymerizable value.

In case the cationically polymerizable groups are epoxy groups, and theradically polymerizable groups are (meth)acrylate groups, one skilledman may also describe the cationically polymerizable/radicallypolymerizable ratio as the epoxy/(meth)acrylate ratio.

The cationically polymerizable/radically polymerizable ratio preferablyranges from 4.5 to 15, or preferably between 5 and 10., or mostpreferably between 5 and 9.

(G) Components with Both Cationically Polymerizable and RadicallyPolymerizable Groups

The composition of the invention may also contain molecules which havemore than one type of reactive functional groups, such that one type offunctional group is capable of cationic homopolymerization while asecond type of functional group on the same molecule is capable ofradical polymerization. Addition of these compounds to the compositionof the present invention gives the unexpected effect of increasedstrength of the green part and improved elongation to break.Cationically polymerizable groups include epoxy, oxetane,tetrahydrofuran, cyclic lactone, cyclic acetal, cyclic thioether, spiroorthoester, and vinylether groups. Hydroxyl groups, which canparticipate in the cationic polymerization as chain transfer agents, arenot included as cationically polymerizable groups since the hydroxylgroups can not be homopolymerized under cationic conditions. Moreover,hydroxyl groups which may be present in these molecules are not expectedto have a strong chain transfer effect on the cationic polymerizationand are for this reason and for reasons of simplicity kept out of thecalculation of the cationically polymerizable/hydroxy ratio. Radicallypolymerizable groups include (meth)acrylates, vinyl groups, andvinylidene groups.

Commercially available materials having cationically polymerizable andfree-radically polymerizable functional groups include the “Cyclomer”series, such as Cyclomer M-100, M-101, or A-200 (available from DaicelChemical, Japan), Ebecryl-3605 (available from Radcure Specialties),VEEA or VEEM (available from Nippon Shobukai Co. Ltd. of Osaka, Japan),and CD611, SR531 or SR285 (available from Sartomer).

Components with both cationically polymerizable and radicallypolymerizable groups are generally present in an amount from 0-25 wt %,preferably between 1 and 20 wt %, more preferably in a range between 3and 15 wt %.

The above compounds having both cationically polymerizable and radicallypolymerizable groups are included in the calculation of the cationicallypolymerizable/hydroxy ratio and the cationically polymerizable/radicallypolymerizable ratio.

(H)Additives/Other Components

Additives may also be present in the composition of the invention.Stabilizers are often added to the compositions in order to prevent aviscosity build-up, for instance a viscosity build-up during usage in asolid imaging process. Preferred stabilizers include those described inU.S. Pat. No. 5,665,792, the entire disclosure of which is herebyincorporated by reference. Such stabilizers are usually hydrocarboncarboxylic acid salts of group IA and IIA metals. Most preferredexamples of these salts are sodium bicarbonate, potassium bicarbonate,and rubidium carbonate. Rubidium carbonate is preferred for formulationsof this invention with recommended amounts varying between 0.0015 to0.005% by weight of composition. Alternative stabilizers arepolyvinylpyrrolidones and polyacrylonitriles. Other possibleadditives/other components include dyes, pigments, fillers (e.g. silicaparticles—preferably cylindrical or spherical silica particles-, talc,glass powder, alumina, alumina hydrate, magnesium oxide, magnesiumhydroxide, barium sulfate, calcium sulfate, calcium carbonate, magnesiumcarbonate, silicate mineral, diatomaceous earth, silica sand, silicapowder, titanium oxide, aluminum powder, bronze powder, zinc powder,copper powder, lead powder, gold powder, silver dust, glass fiber,titanic acid potassium whisker, carbon whisker, sapphire whisker,beryllia whisker, boron carbide whisker, silicon carbide whisker,silicon nitride whisker, glass beads, hollow glass beads, metaloxidesand potassium titanate whisker), antioxidants, wetting agents,photosensitizers for the free-radical photoinitiator, free-radical chaintransfer agents, leveling agents, defoamers, surfactants and the like.

Aromatic and Cycloaliphatic Content.

The compositions of the present invention preferably have a rather highcontent of aromatic and/or cycloaliphatic groups. It has been found thata high content of these groups improves the modulus of the cured object,without the need for a high cross-link density, while keeping the Izodand/or K1c-value high, especially in combination with an cationicallypolymerizable/hydroxy ratio between 2.5 and 5.0.

The aromatic and cycloaliphatic content of the formulation can bedetermined by counting the number of aromatic and cycloaliphatic groupscontained in each component in the composition. For each aromatic group,independent of the substitution, an average molecular weight of 76 g/molis used. The molecular weight of a cycloaliphatic group is defined asthe weight of the cycloaliphatic ring fragment of the cycloaliphaticgroup. In case a cycloaliphatic group is a cyclohexylgroup, a molecularweight of 82 g/mol is assumed (The weight of possible substituents isnot calculated to be part of the weight of the cyclohexylgroup).

For each component in the formulation the content of aromatic andcycloaliphatic groups can be calculated by summing the weight of allaromatic and cycloaliphatic groups of the component and dividing this bythe molecular weight of the component. This is the weight fractionarom/cycloaliph of a component.

Next, the content of aromatic and cycloaliphatic groups of the totalcomposition can be calculated by summing the weight of each component in100 g composition, multiplied by the weight fraction arom/cycloaliph ofeach component in the composition.

Preferably, the aromatic and cycloaliphatic content of the formulationis between 0.2 and 0.6, more preferably between 0.25 and 0.5, even morepreferably between 0.3 and 0.45 and most preferably between 0.32 and0.40.

Cross-Link Density

The compositions preferably have a medium cross-link density. It hasbeen found that having a high cross-link density causes embrittlement ofthe composition. A measure for the cross-link density can beconveniently determined by examining the value of the storage modulus E′at 200° C., as measured with dynamic mechanical analysis in tension witha frequency of 1 Hz. Preferably, the storage modulus E′ at 200° C.ranges between 2 and 35 MPa, more preferably between 4 and 30 MPa, evenmore preferably between 6 and 25 MPa and most preferred between 8 and 20MPa.

Formulations According to the Invention

The present application claims resin compositions comprising certaincomponents that—after full cure—give objects that have uniqueproperties. The present invention is exemplified with many examples,which should not be regarded as limiting the scope of the presentinvention. The skilled man in the art may make alternative compositionsthat fall under the claims but may be different from the disclosedexamples. One way of designing alternative compositions is by applyingthe following design procedure. The skilled man can make use of a twostep design process, in which he first designs a matrix material (whichcontains the components from the composition except the impact modifierd). In this design process, a matrix material is developed which issusceptible to impact modification. This involves selection of acombination of components (all components except impact modifier d) suchthat a matrix material is obtained which when cured has a tensilemodulus at room temperature of at least 2 GPa (preferably higher than2.5 GPa, more preferably higher than 3 GPa) and a yield stress lowerthan 85 MPa, preferably lower than 80 MPa, more preferably lower than 75MPa.

The development of such a matrix can be guided by selecting combinationsof components a, b and c such that

-   1. the molar ratio of cationically polymerizable groups and hydroxyl    groups is preferably between 2.0 and 5.0, more preferably from 2.2    to 4.75 and most preferably from 2.4 to 4.5,-   2. the aromatic and cycloaliphatic content is preferably between 0.2    and 0.6, more preferably between 0.25 and 0.5 and even more    preferably between 0.3 and 0.45, and most preferably between 0.32    and 0.40.    In the case a hybrid formulation is designed, e.g. for    stereolitographic applications and additional design guideline is to    have:-   3. a molar ratio of cationically polymerizable groups and radically    polymerizable groups preferably between 4.5 and 15, more preferably    between 5 and 10 and most preferably between 5 and 9.    When formulated according to these guidelines a matrix material is    obtained which has a proper balance of stiffness on the one hand and    a sufficiently low yield stress to show yielding behavior during a    tensile test. A further consequence of following these guidelines    (esp. the target ratio of cationically polymerizable groups and    hydroxyl groups) is that after curing a network with intermediate    cross-link density is obtained. As described above this can be seen    from the value of the storage modulus E′ of the cured material at    200° C., measured with dynamic mechanical analysis at 1 Hz, which is    preferably between 2 and 35 MPa, more preferably between 4 and 30    MPa, even more preferably between 6 and 25 MPa, and most preferred    between 8 and 20 MPa. Following the guideline of the aromatic and    cycloaliphatic content is preferred to obtain sufficient modulus by    preventing the glass transition temperature from dropping below room    temperature.    In the second step, the fracture toughness and/or the impact    resistance of the material is improved by adding component d to the    formulation in such an amount and type that the desired properties    (as claimed) are obtained.    The comparative examples in this patent application show that parts    may be obtained that have too low toughness (this is low K1c or Izod    values) when the molar ratio of the cationically polymerizable    groups and hydroxyl groups is too high, or the molar ratio of    cationically polymerizable groups and radically polymerizable is too    low. In other comparative experiments it is shown that when the    aromatic and cycloaliphatic content is too low and or the molar    ratio of the cationically polymerizable groups and hydroxyl groups    is too low that parts are obtained that show rubbery behavior of the    fully cured material at room temperature. Finally, in some cases no    impact modifier is used, which also results in parts having too low    K1C and/or Izod values.

Applications

The present compositions are suitable for a wide variety ofapplications. For instance, the compositions can be used to prepare athree dimensional object by rapid prototyping. Rapid prototyping,sometimes also referred to as “solid imaging” or “stereolithography”, isa process wherein a photoformable composition is coated as a thin layerupon a surface and exposed imagewise to actinic radiation such that thecomposition solidifies imagewise. This coating is most conveniently doneif the composition is a liquid at room temperature, but a solidcomposition may also be melted to form a layer, or a solid or pastecomposition may be coated if it shows shear thinning behavior.Subsequently, new thin layers of photoformable composition are coatedonto previous layers of exposed and unexposed composition. Then the newlayer is exposed imagewise in order to solidify portions imagewise andin order to induce adhesion between portions of the new hardened regionand portions of the previously hardened region. Each imagewise exposureis of a shape that relates to a pertinent cross-section of aphotohardened object such that when all the layers have been coated andall the exposures have been completed, an integral photohardened objectcan be removed from the surrounding composition.

Accordingly, a rapid prototyping process can for instance be describedas:

-   (1) coating a thin layer of a composition onto a surface;-   (2) exposing said thin layer imagewise to actinic radiation to form    an imaged cross-section, wherein the radiation is of sufficient    intensity and time to cause substantial curing of the thin layer in    the exposed areas;-   (3) coating a thin layer of the composition onto the previously    exposed imaged cross-section;-   (4) exposing said thin layer from step (3) imagewise to actinic    radiation to form an additional imaged cross-section, wherein the    radiation is of sufficient intensity and time to cause substantial    curing of the thin layer in the exposed areas and to cause adhesion    to the previously exposed imaged cross-section;-   (5) repeating steps (3) and (4) a sufficient number of times in    order to build up the three-dimensional article.

In general, the three-dimensional article formed by exposure to actinicradiation, as discussed above, is not fully cured, by which is meantthat not all of the reactive material in the composition has reacted.Therefore, there is often an additional step of more fully curing thearticle. This can be accomplished by further irradiating with actinicradiation, heating, or both. Exposure to actinic radiation can beaccomplished with any convenient radiation source, generally a UV light,for a time ranging from about 10 to over 60 minutes. Heating isgenerally carried out at a temperature in the range of about 75-150° C.,for a time ranging from about 10 to over 60 minutes.

For the present invention postcuring is performed during 60 minutesexposure in a UV-postcure apparatus without additional heating, toobtain a fully cured article, unless otherwise specified (see examples1-3)

K_(1C) and Izod Values.

The cured articles made from the resin composition of the presentinvention have—after full cure—high toughness in combination with a highE-modulus. Toughness can be determined by a number of different methods,of which the Izod (impact resistance) is the best known method. Thecured articles according to the invention have an Izod of least 0.45J/cm, preferably at least 0.5 J/cm, more preferably at least 0.55 J/cm,more preferably at least 0.6 J/cm, even more preferably at least 0.8J/cm.

An alternative measure for toughness is resistance against crackpropagation, which can be determined by measuring the K_(1C)-value. TheK_(1C)-value of cured articles described in the state of the art isalways below 1 MPa·(m)¹¹², when an E-modulus of 2 GPa (2000 MPa) orlarger is measured. The articles made from the resin compositionsaccording to the invention have a K_(1C)-value of at least 1.3Mpa·(m)^(1/2), preferably at least 1.6 MPa·(m)^(1/2), more preferably atleast 1.9 MPa·(m)^(1/2), and most preferred at least 2.5 MPa·(m)^(1/2).

EXAMPLES

TABLE 1 Materials List Material Name Material Description Vendor Epon825 Bisphenol A Diglycidyl Ether Epoxy Resolution Performance ResinProducts Cyracure UVR-6105 3,4-Epoxy Cyclohexyl Methyl-3,4-Epoxy DowChemical Cyclohexyl Carboxylate Ebecryl 3605 Partially acrylatedBisphenol-A epoxy UCB/Cytec resin Oxetane OXT-1013-ethyl-3-hydroxymethyl-oxetane Toagosei Vinylether ethyl 2-(2-Vinyloxyethoxy)ethyl acrylate Nippon Shokubai Co. Ltd. acrylateEbecryl 3700 Bisphenol-A epoxy diacrylate UCB/Cytec SR-399Dipentaerythritol Pentaacrylate Esters Sartomer SR 349 Bisphenol AEthoxylate Diacrylate Sartomer SynFac 8025U Polyalkoxylated Bisphenol AMilliken Chemical SynFac 8009 Polyalkoxylated Bisphenol A MillikenChemical Stepanpol PS2002 Di[(diethylene glycol) o-phthalate] StepanCompany Emulgen BPA-5 Polyalkoxylated Bisphenol A Kao SpecialtiesAmericas Bisphenol A Polyalkoxylated Bisphenol A Aldrich (ethoxylate)4,Average Mn = 404 g/mol EO(4)BPA Triethylene Glycol Aldrich Pluracol TP440 Propoxylated Trimethylolpropane BASF Terathane 1000Poly(tetramethylene ether) glycol Invista Placcel 220EBPoly(hexamethylene carbonate) diol Daicel CAS#61630-98-6 Average Mn =2000 g/mol Propylene Carbonate Aldrich BYK A 501 Antifoam solution,silicone free BYK Chemie Silwet L7600 Polyalkyleneoxide modified GESilicones - OSI polydimethylsiloxane Specialties Chivacure 1176Arylsulfonium Hexafluoroantimonate Chitec Rhodorsil 2074 Aryliodoniumtetrakis pentafluorophenyl Rhodia borate Chivacure BMS4-Benzoyl-4′-methyldiphenyl sulfide Chitec Irgacure 1841-Hydroxycyclohexyl phenyl ketone Ciba Additives Paraloid EXL-2314Acrylic core-shell polymer Rohm and Haas Paraloid EXL-2600 Acryliccore-shell polymer Rohm and Haas Durastrength D400 Acrylic core-shellpolymer Arkema SR-9003 Propoxylated Neopentyl Glycol Sartomer DiacrylateParaloid KM-365 Acrylic core-shell polymer Rohm and Haas Albidur EP 2240Polysiloxane particles in epoxy Hanse Chemie Terathane 250poly(tetramethylene ether) glycol Invista DPHA Dipentaerythritolhexacrylate ester Sartomer

Preparation of Epoxy Formulations: (Table 4), Examples 1-3

A mixture of the epoxy and the polyol components was heated toapproximately 60° C. and stirred with a magnetic stirrer for 5 minutes.In the next step, the impact modifier was slowly added to theformulation while continuing stirring. After completion of thisaddition, the formulation was heated to 100° C. and continuously stirredovernight to obtain a good dispersion. Treating the mixture with anUltra-Turrax T25 dispersing instrument further optimized the dispersionquality. Three pulses of 20 seconds were applied. After this treatmentthe liquid resin was cooled to 70° C. after which the photo initiatorwas added and the complete formulation was stirred with a magneticstirrer for 5 minutes. Finally, the liquid resin was cooled to roomtemperature.

Bulk Molding: (Examples 1-3)

Thick parts (tensile and K_(1C) fracture toughness bars) were preparedby bulk molding, using a rubber mold with predefined sample shapes.Strips with dimensions 60*10*4 mm and 150*30*4 mm (L*W*T) were preparedfrom which K_(1C) and tensile bars, respectively, were machined.

In order to prepare thick parts the liquid resin formulation was pouredinto the mold in four subsequent fillings, each with a layer thicknessof about 1 mm, with intermediate UV-curing. Curing was applied bypassing the mold at room temperature, in open air, three times through ahome built UV-rig equipped with a 400 Watt medium pressure Hg bulb. Anintegral UV dose of 6 J/cm² was applied to each layer. The dose wasmeasured with an International Light IL390 Light Bug.

Post Baking: (Examples 1-3)

Post cure was performed by storing the samples for approximately 20 h at80° C. in a hot air oven. After post cure the samples were stored for atleast a week at room temperature (23° C.) and 50% relative humiditybefore the testing was performed. K_(1C) and tensile testing of thesesamples was performed under the same environmental conditions.

Preparation of Hybrid Formulations—Examples 4-10, ComparativeExperiments A-D. Preparation of Dispersions (Table 4 and Table 5a, 5band 5c)

Core-shell powders were added to epoxy resin with gentle stirring andmixed until the powders were wetted. The slurry was transferred to themix can of a three-shaft Versamixer manufactured by Charles Ross & Sons.The slurry was mixed at 60 rpm with the anchor mixer, while the waterjacket was heated with hot water. When the slurry temperature reached35° C., the disperser speed was set to 5000 rpm and the water flow tothe water jacket was stopped. When the slurry temperature rose to 45°C., the disperser speed was raised to 6500 rpm and the emulsifier speedwas set at 5500 rpm. The mix can was evacuated to a vacuum of 948 mbaronce the temperature reached 60° C. When the temperature reached 80-82°C., the disperser and emulsifier were turned off and the mixture wascooled by flowing cold water through the water-jacket. Once thetemperature fell below 50° C., the anchor agitator was turned off andair was re-admitted to the mix can.

TABLE 2 Examples of Core-Shell Dispersions D1 D2 D3 D4 D5 D6 UVR 6105(%) 62.7 80 80 52.6 Epon 825 (%) 20.2 80 80 27.4 EXL-2314 (%) 17.1 20 2020 20 KM-365 (%) 20 Used in 9 4, 7, B, C 5, 7, 8 5, 7, 8 4, 7, B, C 10Example/comparative experiment

Preparation of Formulations

The individual components were weighed out and added into a suitablecontainer. Several components (the core-shell/epoxy dispersions, Ebecryl3605, and Stepanpol) were warmed to 55° before being weighed out andblended. Mixing was accomplished over 6-16 hours at ambient temperatureusing a propeller type mixing blade. Formulations were degassed byimmersion in an ultrasonic bath at 30-40° C. The compositions of theExample and Comparative Experiment formulations are listed in Tables 5and 6.

Working Curve Measurement

The exposure response for each formulation was measured using a 20 gsample of the formulation in a 100 mm diameter Petri dish held at 30° C.and 30% RH. The surface of the formulation was exposed with a beam froma laser; either an argon-ion laser operating with the wavelengths of333, 351, and 364 nm or a solid state laser operating at a wavelength of354 nm can be used. The exposures were made in half-inch squares whichwere scanned out by drawing consecutive parallel lines approximately50.8 micron apart on the surface of the liquid in the petri-dish. Thespot diameter at the liquid surface was approximately 0.0127 cm indiameter (1/e²). After waiting at least 15 minutes for the exposedpanels to harden, the panels were removed from the Petri dish andexcess, uncured resin was removed by blotting with a Kimwipe EX-L(Kimberly Clark). Film thickness was measured with a Mitutoyo ModelID-C112CE Indicator Micrometer. Film thickness is a linear function ofthe logarithm of the exposure energy; the slope of the regression is Dp(units of micron) and the intercept is Ec (units of mJ/cm2)

Building Parts

Test formulations were selectively irradiated by a scanned laser beam toform the desired cross-section layer using a Somos Solid State Imager(SSI) or 3D Systems SLA-250 stereolithography machine. The exposureenergy was determined by the laser power, the scanning speed, the laserpulse frequency and the scan line spacing. The exposure energy wasadjusted to yield a target cured layer thickness (cure depth) based onthe Ec and Dp values determined for the resin. The exposed layer wassubmerged under a layer of unpolymerized resin and the exposure step wasrepeated. These exposure and recoat steps were repeated until curedparts were obtained with the desired part thickness. Tables 5 and 6 listthe laser wavelength, coated layer thickness and calculated depth ofcure for the mechanical test parts that were made. Completed parts werelifted out of the formulation vat and removed from their build platform.Uncured resin that was adhered to the parts was washed away with TPM(tripropylene glycol mono methyl ether). The parts were rinsed withisopropanol and dried. Parts were then placed in a post-curing apparatus(“PCA” sold by 3-D Systems, 10 bulb unit using Phillips TLK/05 40 Wbulbs) and exposed to 60 minutes of UV radiation at room temperature.

Tensile Testing

Dog-bone shaped tensile test specimens were built by multiple layerexposure. The samples were nominally 150 mm long, 10.15 mm wide in theirnarrow region and 3.8 mm thick. At least three specimens were built fromeach formulation. Specimens were cleaned, dried and subjected to UVpostcure as described above. Specimens were placed in an environmentcontrolled at 50% RH and 20-23° C. for seven days. Specimens wereremoved from the controlled environment immediately prior to testing.Width and thickness of each specimen were measured with a caliper.Specimens were tested using an MTS Sintech tensile tester following theprocedure of ASTM D638. Samples were held in a set of wedge action gripswith serrated faces; grip separation was 105 mm. Stress was measuredwith a 28.913 kN load cell and strain was measured with an extensometerset to initial gauge length of 25.4 mm. Stress and strain were recordedat a grip separation speed of 5.08 mm/minute. Young's Modulus, %Elongation at Yield, Yield Stress, % Elongation at Break and BreakStress were recorded for each specimen. The average for the threespecimens is reported in Tables 5 and 6. The Young's modulus was takenfrom the slope of the stress-strain curve between 0.05 and 0.25%elongation. The Yield Stress was taken from the maximum in thestress-strain curve (i.e. the Yield point), which usually is foundbetween 2 and 8% elongation. If the sample fails at an elongationbetween 0 and 10%, without showing a maximum in the stress-strain curve,the maximum stress is taken as approximation for the Yield Stress. The %Elongation at Yield is the strain at the yield point. % Elongation atBreak and the Break Stress are taken from the last data point beforefailure of the sample.

Determination of the Critical Stress Intensity Factor K_(1C)

The fracture toughness measurements were performed using the LinearElastic Fracture Mechanics (LEFM) standard for determining K_(C) andG_(C) for plastics, as drafted by the European Group of Fracture (EGF,nowadays called ESIS): J. G. Williams, ESIS: Testing protocol, October1989; A linear elastic fracture mechanics (LEFM) standard fordetermining K_(C) and G_(C) for plastics.

The K_(C) is the critical stress intensity factor at crack propagation.When measured in tensile mode (called mode-1), this toughness parametersis denoted as K_(1C). The measurements were performed using Single EdgeNotch Bend (SENB) specimen. The geometry of the SENB specimen as used isshown in FIG. 1.

Since K_(1C) is a parameter measuring the resistance of a materialagainst crack propagation, it is necessary to pre-crack the specimen.The pre-crack should preferably be straight and sharp. An insufficientsharp pre-crack notch will result in too high K_(1C) values. For theSENB samples the machined notch was further sharpened by tapping a razorblade into the notch. Normally, a sharp pre-crack notch is generated, asthe pre-crack length is at least a few millimetres ahead of the razorblade tip.

Care was taken that the sample dimensions comply with the ESISrequirements as specified in Table 3.

TABLE 3 Geometry requirements for the samples according to ESIS. ESISgeometry Description requirements Sample thickness, B B Ligament width,W 4B > W > 2B Sample length, L L ≧ 4.4W Support&load diameter, D W/4 < D< W Support length, S S = 4W Cut notch length, a a/W = 0.3 Pre-crackednotch length a/W = 0.4-0.6

In practice the sample thickness B, width W and length L may vary fromsample to sample, under the constraint that the ESIS geometryrequirements are met. For the materials of this invention, the preferredrange for B is from 2.5-15 mm, while for W a range from 8-30 mm ispreferred. For samples with K_(1C) of more than 3.5 MPa*√m largerdimensions may be required. The sample length is preferably 4.5-6 timesthe sample width W.

The support length S is adjusted at the beginning of the test to exactly4 times the sample width W. A notch with length a, equal to 0.3 timesthe sample width W, is made with a standard saw, after which thepre-cracked notch is prepared with a rasor blade as described before.

The measurements were performed using a Zwick Z1455 tensile testmachine, controlled with Zwick TestXpert software (version 5.43). Theforce was recorded using a 2 kN force transducer. A displacementtransducer (Zwick long stroke extensometer with a resolution of 0.0025mm/step) was used for measuring the mid-deflection of the beam. Thestandard 3-point bending tools were used to support and to load thesamples in the machine. The applied test speed was 1 mm/min. Thesupport&load diameter was fixed to 6 mm.

Calculation of the Stress Intensity Factor K_(1Q)

The stress intensity factor (K_(1Q)) was calculated using the equationsfrom the ESIS testing protocol for the SENB test piece:

K _(1Q) =f*(F/B)*√W

in which:

f=6*√(a/W)*(1.99−a/W(1−a/W)*(2.15−3.93*a/W+27*(a/W)²)/(1+2*a/W)/(1−a/W)^(3/2)

With:

f: calibration/geometry factor, depending on the a/W ratioF: maximum force at the start of crack propagation.B: thickness of the sampleW: ligament width of the sample

Validity of the Test and Determination of the Critical Stress IntensityFactor K_(1C)

For a valid determination of the critical value of the stress intensityfactor K_(1Q), i.e. the critical stress intensity factor K_(1C), it isrequired that the test specimen dimensions are larger than the plasticzone size, so that any effect of the plastic zone dimensions on thestress intensity analysis can be neglected and a predominantly planestrain state is obtained. This is ensured if the following size criteriaare met: B, a, (W−a)>2.5 (K_(1Q)/σ_(y))²

in which σ_(y) is the yield stress of the material as determined withthe tensile test as describe before. When these conditions are met, thespecimen thickness B is sufficient to ensure plain strain, while thewidth W is sufficient to avoid excessive plasticity in the ligament.

Typically, the test is performed on 3-5 specimens with equal dimensions.The average value of the results from these tests is reported.

Izod Value

Izod impact testing provides an assessment of the ability of materialsto withstand rapidly applied forces such as are encountered from fallingobjects, collisions, drops, etc. The test does not provide engineeringdata about a given material, rather it is best used to compare theimpact resistance of materials formed into a specified specimen shapeand tested under identical conditions.

When comparing the impact resistance of plastic materials, the notchedIzod test, as described in ASTM D 256 is widely used. In this test,specimens are fabricated to a defined geometry and a notch is machinedinto one face of the specimen. The notch simulates the presence in apart of sharp corners, intersecting faces or machined features (such astapped screw holes).

For the notched Izod test, the specimen is held vertically in a visewith the notch parallel to the top of the vise. A pendulum mountedhammer with a defined striking edge is released from a defined heightand swings into the notched face of the specimen at a specified distanceabove the notch. The height attained by the hammer after shearing thespecimen corresponds to the residual energy of the hammer. The hammerenergy lost to the specimen accounts for the energy to make a crack atthe notch tip, to propagate the crack and to propel the broken piece ofthe specimen away from the impact area. The impact energy is determinedas the energy lost by the hammer minus the energy required to propel thebroken piece from the specimen. Results from different materials shouldbe compared only when the geometry, notching technique, notch radius andtesting conditions (equipment, temperature, etc.) are held constant.

Izod Impact testing

Test specimens were built by multiple layer exposure. The samples werenominally 63.5 mm long, 12.7 mm wide and 6.35 mm thick in conformitywith ASTM D-256A. At least five specimens were built from eachformulation. Specimens were cleaned, dried and subjected to UV postcureas described above. Specimens were left at ambient conditions for twodays before notching. Specimens were notched according to ASTM D-256Ausing a CS-93M Sample Notcher from CSI. The notched samples were placedin an environment controlled at 50% RH and 20-23° C. for two days.Specimens were removed from the controlled environment immediately priorto testing. Izod Impact values were measured with a Zwick model 5110impact tester fitted with a 2.75 J pendulum.

Determination of the Dynamic Storage Modulus E′ at 200° C.

The dynamic storage modulus of the material of the present invention ismeasured by DMTA in tension according to ASTM D5026-95a “Standard TestMethod for Measuring the Dynamic Mechanical Properties of Plastics inTension”, under the following conditions, which are adapted for thecoatings of the present invention.

A temperature sweep measurement is carried out under the following testconditions:

Test pieces: Rectangular stripsLength between grips: 18-22 mm

Width: 4 mm

Thickness: between about 50 and 1000 μmEquipment: Tests were performed on a DMTA machine from TA instrumentstype RSA3

Frequency: 1 Hz

Initial strain: 0.15%Temperature range: starting from −130° C. heating until 250° C.Ramp speed: 5° C./min

Autotension: Static Force Tracking Dynamic Force

-   -   Initial static Force: 0.9N    -   Static>Dynamic Force 10%        Autostrain: Max. Applied Strain: 2%    -   Min. Allowed Force: 0.05N    -   Max. Allowed Force: 1.4N    -   Strain adjustment: 10% (of current strain)        Dimensions test piece: Thickness: measured with an electronic        Heidenhain thickness measuring device type MT 30B with a        resolution of 1 μm.        Width: measured with a MITUTOYO microscope with a resolution of        1 μm.

All the equipment was calibrated in accordance with ISO 9001. Beforestarting the measurement each rectangular strip was dried for 5 minutesat room temperature in a nitrogen atmosphere

In a DMTA measurement, which is a dynamic measurement, the followingmoduli are measured: the storage modulus E′, the loss modulus E″, andthe dynamic modulus E* according to the following relationE*=(E′²+E″²)^(1/2).

The value of the storage modulus E′ in the DMTA curve at a temperatureof 200° C., measured at a frequency of 1 Hz under the conditions asdescribed in detail above, is taken.

TABLE 4 Examples of epoxy formulations Example 1 2 3 EPON 825 (%) 58.858.8 58.8 Emulgen (%) 31.7 31.7 31.7 EXL2600 (%) 9.0 EXL2314 (%) 9.0Albidur EP 2240 (%) 9.0* Chivacure (%) 0.5 0.5 0.5 Cat. Poly./Hydroxy2.34 2.34 2.34 Content aromatic and 0.36 0.36 0.36 cycloaliphatic E[GPa] 2.2 2.3 2.2 Yield [MPa] 44 47 41 K_(1Q) (MPa*m^(1/2)) 1.43 2.551.44 Specimen width W 8.9 8.9 8.9 (mm) Specimen thickness B 3.34 2.992.79 (mm) K_(1c) [MPa*m^(1/2)] 1.43 >1.63** >1.37** *Denotes weight % ofpolysiloxane particles from the Albidur EP 2240. The epoxy portion ofthe Albidur is included in the weight % Epon 825. **Specimen thicknessfor examples 2 and 3 is less than the lower limit for a valid K_(1c)detemination. Consequently, the critical value is expected to be lowerthan the value of K_(1Q). For K_(1c) we therefore specify the maximumvalid value that can be determined with this sample thickness, given thelevel of the yield stress of the material. This value serves as a lowerlimit for the K_(1c) of the material.

TABLE 5a Examples of hybrid formulations Example 4 5 6 7 8 9 10 UVR 6105(%) 40.87 30.70 40.87 31.69 20.00 37.81 30.70 Epon 825 (%) 10.22 16.0020.44 18.39 29.00 12.17 16.01 Chivacure 1176 (%) 2.26 3.32 2.26 2.263.30 3.29 3.30 SynFac 8025U (%) 15.33 13.00 15.33 9.50 6.70 8.44 13.00Stepanpol PS2002 (%) 10.22 5.40 6.34 10.00 4.15 5.40 Triethyleneglycol(%) 4.34 4.25 4.34 4.34 4.25 4.22 4.25 EXL-2314 (%) 5.11 9.00 5.11 7.158.00 10.34 KM-365 (%) 9.00 SR399 (%) 4.34 4.25 4.34 4.34 4.25 4.13 4.25SR-9003 (%) 2.00 Irgacure 184 (%) 1.99 2.30 1.99 1.99 2.30 2.26 2.30Ebecryl 3605 (%) 5.11 11.6 5.11 13.80 12.00 10.98 11.60 Silwet 7600 (%)0.13 0.13 0.13 0.13 0.13 0.13 0.13 BYK 501 (%) 0.07 0.07 0.07 0.07 0.070.07 0.07 Cat. Poly./Hydroxy 2.82 3.14 4.35 3.56 3.13 4.10 3.15 Cat.Poly./Rad. Poly. 7.46 5.43 8.55 5.36 5.19 6.17 5.43 Content Aromatic0.38 0.35 0.40 0.36 0.33 0.36 0.35 &Cycloaliphatic Build InformationMachine SSI SLA SSI SSI SSI SSI SSI 250 Laser Type/ Ar+/ Solid SolidAr+/ Solid Solid Solid Wavelength (nm) 351 State/ State/ 351 State/State/ State/ 354.7 354.7 354.7 354.7 354.7 Cure Depth (μm) 304.8 254304.8 304.8 254 304.8 254 Layer Thickness (μm) 152.4 101.6 152.4 152.4127 152.4 127 Modulus (MPa) 2200 2549 2900 2700 2200 2170 2000 YldStress (MPa) 35 48 56 50 41 41 34 Elongation at Break % 14 12.6 7 9.4 2432 25 Izod (J/cm) 0.59 0.54 0.47 0.48 0.51 0.49 0.94 K_(1Q)(MPa*m^(1/2)) 2.9 2.3 3.3 Specimen width W 21.3 12.2 12.2 (mm) Specimenthickness B 10.4 5.87 5.94 (mm) K_(1c) (MPa*m^(1/2)) 2.9 2.3 >2.0**Specimen thickness for example 9 is less than the lower limit for avalid K_(1c) detemination. Consequently, the critical value is expectedto be lower than the value of K_(1Q). For K_(1c) we therefore specifythe maximum valid value that can be determined with this samplethickness, given the level of the yield stress of the material. Thisvalue serves as a lower limit for the K_(1c) of the material

TABLE 5b Examples of hybrid formulations Example 11 12 13 14 15 UVR 6105(%) 30.7 27.2 30.7 30.8 30.7 Epon 825 (%) 16 16 21 16.05 15 Oxetane OXT101 (%) 3 Vinylether ethyl acrylate 5.2 (%) Chivacure 1176 (%) 3.3 3.33.3 3.3 Rhodorsil 2074 (%) 1.0 Chivacure BMS (%) 0.33 Propylenecarbonate (%) 1.66 SynFac 8025U (%) 13 13 13 11.5 Synfac 8009 (%) 13Stepanpol PS2002 (%) 5.4 5.4 6 5.42 5.1 Triethyleneglycol (%) 4.25 4.254.85 4.26 Propoxylated 7.55 trimethyloipropane Pluracol TP440 (%)EXL-2314 (%) 9 9 9 9 9 SR399 (%) 4.25 4.25 4.5 4.26 4.25 Irgacure 184(%) 2.30 2.30 2.30 2.31 2.30 Ebecryl 3605 (%) 11.6 11.6 11.64 11.1Silwet L7600 (%) 0.13 0.13 0.13 0.13 0.13 BYK A501 (%) 0.07 0.07 0.070.07 0.07 Cat. Poly./Hydroxy 2.8 2.4 3.2 3.1 3.2 Cat. Poly./Rad. Poly.5.43 5.46 5.65 5.43 5.42 Content Aromatic 0.36 0.33 0.33 0.35 0.34&Cycloaliphatic Build Information Machine SSI SSI SSI SSI SSI LaserType/Wavelength Solid Solid Solid Solid Solid (nm) State/ State/ State/State/ State/ 354.7 354.7 354.7 354.7 354.7 Cure Depth (μm) 254 254 254254 254 Layer Thickness (μm) 127 127 127 127 127 Modulus (MPa) 2596 24982071 2353 2787 Yld Stress (MPa) 38 45 34 41 47 Elongation at break (%)10.7 31 48 34 12 Izod (J/cm) 0.56 0.79 0.84 0.55 0.50 K_(1Q)(MPa*m^(1/2)) Specimen width W (mm) Specimen thickness B (mm) K_(1c)(MPa*m^(1/2))

TABLE 5c Examples of hybrid formulations Example 16 17 18 UVR 6105 (%)27.05 22.1 35 Epon 825 (%) 18.56 22.1 18 Oxetane OXT 101 (%) 2.25Chivacure 1176 (%) 3.37 3.5 3.5 SR 349 (%); BPA(EO)3DA 1.17 9.7 11.9Placcel 220EB (%) 4.25 13.5 10 BPA (EO)4 (%) 4.69 22 SynFac 8025U (%)9.75 10.7 Stepanpol PS2002 (%) 4.05 Triethyleneglycol (%) 3.19 3.9EXL-2314 (%) 6.75 SR399 (%) 3.77 4.6 4.4 Irgacure 184 (%) 2.32 2.3 2.4Ebecryl 3605 (%) 8.7 Silwet L7600 (%) 0.1 0.13 0.13 BYK A501 (%) 0.050.07 0.07 Cat. Poly./Hydroxy 2.7 2.4 4 Cat. Poly./Rad. Poly. 5.95 5.15.6 Content Aromatic &Cycloaliphatic 0.34 0.35 0.37 Build InformationMachine SSI 3D- 3D- systems systems Viper Viper Laser Type/Wavelength(nm) Solid Solid Solid State/ State/ State/ 354.7 354.7 354.7 Cure Depth(μm) 254 254 254 Layer Thickness (μm) 127 152.4 152.4 Modulus (MPa) 20412030 2300 Yld Stress (MPa) 41.2 43.7 56.0 Elongation at break (%) 16.218.3 13.0 Izod (J/m) 0.66 0.45 0.45 K_(Q) (MPa*m^(1/2)) 3.0 1.9 Specimenwidth W (mm) 21.3 21.3 Specimen thickness B (mm) 10.7 10.2 K_(1c)(MPa*m^(1/2)) >2.85 1.9Examples 17 and 18 have been postbaked at 80 C during 24 hours after theUV postcure.

TABLE 6a Comparative Experiments: hybrid formulations Comparativeexperiments A B C D Epon 825 (%) 14.25 20.44 14.70 1.80 UVR 6105 (%)44.26 40.87 43.29 56.90 Chivacure 1176 (%) 3.85 2.26 3.67 4.94 StepanpolPS2002 (%) 4.85 0.00 4.62 SynFac 8025U (%) 4.94 5.11 9.42 Terathane 1000(%) 14.97 Triethyleneglycol (%) 4.94 4.34 4.71 EXL-2314 (%) 5.11 AlbidurEP 2240 (%) 1.20* SR399 (%) 4.84 4.34 4.61 SR-9003 (%) 2.34 Ebecryl 3700(%) 17.97 Ebecryl 3605 (%) 12.85 15.33 12.24 Irgacure 184 (%) 2.65 1.992.53 2.00 BYK 501 (%) 0.08 0.07 0.07 0.02 Silwet 7600 (%) 0.16 0.13 0.150.20 Cat. Poly./Hydroxy 4.72 6.47 4.23 15.42 Cat. Poly./Rad. Poly. 6.166.28 6.38 6.73 Content Aromatic 0.41 0.41 0.41 0.37 &CycioaliphaticBuild Information Machine SSI SSI SSI SSI Laser Type/wavelength SolidAr+/351 Solid Solid State/ State/ State/ 354.7 354.7 354.7 Cure Depth(μm) 304.8 304.8 304.8 330.2 Layer Thickness (μm) 152.4 152.4 152.4152.4 RT, 7 days Modulus (MPa) 3526 3045 3087 2604 Yld Stress (MPa) 6958 58 54 Elongation at Break % 5.7 4.1 11.2 7.6 Izod Impact (J/cm) 0.1750.225 0.21 0.24 no impact Cat. no impact Cat. modifier Poly/ modifierPoly/ Hydroxy Hydroxy high high

TABLE 6b Comparative Experiments: hybrid formulations Comparativeexperiments E F G Prior art document EP938026 EP938026 EP938026 Examplein document 1 7 8 UVR 6110 (%) 30 27 UVR 6199 (%) 5 25 28 Epolite 1600(%) 3 TMPTA (%) 25 13 25 Sunnix GP-400 (%) 15 13 12 RKB rubber particles16 8 15 Epolite 1500 NP (%) 10 16 Photoinitiators 6 4 4 Cat.Poly./Hydroxy 2.4 4.3 3.2 Cat. Poly./Rad. Poly. 1.1 3.2 1.1 ContentAromatic & 0.19 0.25 0.11 Cycloaliphatic Properties Modulus (MPa) 15801800 1420 Izod Impact (J/cm) 0.52 0.48 0.52 Remarks Modulus too Modulustoo Modulus too low low low Cause Arom/cycl Cat. Poly/Rad. Aromicyclcontent low Poly low content low

TABLE 6c Comparative Experiments: hybrid formulations Comparativeexperiments H I Prior art document US2004013977 US2004013977 Example inprior art 2 7 UVR 6110 (%) 47.6 56.9 Araldyte DY-T (%) 20 15 SumisolBPRE (%) 10 10 TMP (%) 2 2 Ebecryl 3700 (%) 16.5 13.5 Photoinitiators3.5 2.6 Additives 0.4 Cat. Poly./Hydroxy 7.1 7.5 Cat. Poly./Rad. Poly.8.1 10.4 Content Aromatic 0.35 0.39 &Cycloaliphatic Properties Modulus(MPa) 1900 1600-2100 Izod Impact (J/cm) 0.4 0.42 Remarks Modulus andimpact Impact too low too low Cause Cat. Poly/Hydroxy high + Cat.Poly/Hydroxy high + no impact modifier d no impact modifier d PI's,additives and rubber particles not included in calculation of CatPoly/Hydroxy ratio, Cat. Poly./Rad. Poly. ratio and Content Aromatic &Cycloaliphatic groups.Tables 6b and 6c show resin compositions as disclosed in prior artdocuments that however do not generate articles that show the desiredproperties as disclosed in the present invention.

1-32. (canceled)
 41. A radiation curable resin composition comprising:a) a cationically polymerizable component comprising at least one epoxygroup; b) a cationic photoinitiator; c) a hydroxy component; and d) 1 to30 wt %. of an impact modifier selected from the group consisting ofelastomers based on copolymers of ethylene and one or more C2 to C12α-olefin monomers, elastomers based on copolymers of propylene and oneor more C2 to C12 α-olefin monomers, styrene/butadiene random copolymer,styrene/isoprene random copolymer, ethylene/acrylate random copolymers,acrylic block copolymers, styrene/butadiene/(meth)acrylate blockcopolymers, styrene/butadiene block copolymer, styrene-butadiene-styreneblock copolymer, and styrene-isoprene-styrene block copolymer.
 42. Theradiation curable resin composition of claim 41 wherein the impactmodifier comprises a styrene/butadiene/(meth)acrylate block copolymer.43. The radiation curable resin composition of claim 41 wherein theimpact modifier comprises an acrylic block copolymer.
 44. The radiationcurable resin composition according to claim 41, wherein the elastomersare modified to contain reactive groups comprising epoxy, oxetane,carboxyl or hydroxyl.
 45. The radiation curable resin composition ofclaim 41 wherein the cationically polymerizable/hydroxy ratio of thecomposition is in the range of from 2 to
 5. 46. The radiation curableresin composition of claim 41 wherein the cationicallypolymerizable/radically polymerizable ratio is in the range of from 4.5to
 15. 47. The radiation curable resin composition of claim 41 wherein,the cationically polymerizable/hydroxy ratio of the composition is inthe range of from 2.2 to 4.75.
 48. The radiation curable resincomposition of claim 47 wherein the cationically polymerizable/radicallypolymerizable ratio is in the range of from 5 to
 10. 49. The radiationcurable resin composition of claim 41 wherein the cationicallypolymerizable/hydroxy ratio of the composition is in the range of from2.4 to 4.5.
 50. The radiation curable resin composition of claim 41wherein the resin composition after full cure has a tensile modulusof >2 GPa; a yield stress <70 MPa; and a Ki_(C) value >1.3 MPa·(m)¹⁷² oran Izod value >0.45 J/cm.
 51. The radiation curable resin composition ofclaim 41, wherein the hydroxy component is selected from the groupconsisting of polyoxyethylene glycols of molecular weights from about200 to about 10,000; polyoxypropylene glycols of molecular weights fromabout 200 to about 10,000; triols of molecular weights from about 200 toabout 10,000; polytetramethylene glycols; poly(oxyethylene-oxybutylene)random copolymer; poly(oxyethylene-oxybutylene) block copolymers;hydroxy-terminated polyesters; hydroxy-terminated polylactones;hydroxy-functionalized polyalkadienes; aliphatic polycarbonate polyols;hydroxy-terminated polyethers; and a chemical of the followingstructure:

wherein R3=—CH₂—, —C(CH₃J₂-, —C(CF₃)₂—, —CCl₂—, —O—, —S—, andR4=—CH₂CH₂— or —CH₂CH(CH₃)—, and n and m are 1 through
 10. 52. Theradiation curable resin composition of claim 41, wherein the compositioncontains 1-30 wt % of a radically polymerizable compound and 0.1-15 wt %of a free radical photoinitiator.
 53. The radiation curable resincomposition of claim 52, wherein the radically polymerizable compoundcomprises a polyfunctional acrylate.
 54. The composition according toclaim 41, wherein the composition comprises 1-15 wt % of a componenthaving at least one epoxy group and at least one (meth)acrylate group.55. The radiation curable resin composition of claim 41, wherein thecomposition comprises a aromatic/cycloaliphatic content between 0.2 and0.6.
 56. The radiation curable resin composition of claim 41, whereinthe composition contains a filler.
 57. A three-dimensional articleformed from the radiation
 58. A process for making three dimensionalarticles comprising the steps of (1) coating a thin layer of acomposition onto a surface; (2) exposing said thin layer imagewise toactinic radiation to form an imaged cross-section, wherein the radiationis of sufficient intensity and time to cause substantial curing of thethin layer in the exposed areas; (3) coating an additional thin layer ofthe composition onto the imaged cross-section; (4) exposing saidadditional thin layer from step (3) imagewise to actinic radiation toform a new imaged cross-section, wherein the radiation is of sufficientintensity and time to cause substantial curing of the additional thinlayer in the exposed areas and to cause adhesion of the new imagedcross-section to the imaged cross-section, wherein the new imagedcross-section becomes part of the imaged cross-section; (5) repeatingsteps (3) and (4) a sufficient number of times in order to build up thethree-dimensional article, wherein the composition is defined accordingto claim
 41. 59. A radiation curable resin composition comprising: a) acationically polymerizable component comprising at least one epoxygroup; b) a cationic photoinitiator; c) a hydroxy component; and d) animpact modifier selected from the group consisting of a SBM blockcopolymer, a SBS block copolymer, a SEBS block copolymer, a SIS blockcopolymer, a SEPS block copolymer, an ethyl/acrylate random copolymer, aglycidyl methacrylate modified random ethylene/acrylate copolymer, and amaleic anhydride modified random ethylene/acrylate copolymer.
 60. Athree-dimensional article formed from the radiation curable resin ofclaim 59.